1. Field Of The Invention
The present invention relates to a method and a machine for making hollow reinforcing members formed by fibers distributed in three dimensions. It also relates to reinforcing members made in this way, and to composite parts obtained by using said reinforcing members impregnated with a settable binder.
2. Background Art
Methods of making such reinforcing members are already known which consist of in winding a two-dimension substrate onto a mandrel with said fibers being distributed in the substrate in at least two directions, with the third fiber dimension being added by needling said substrate. Such methods are described, for example, in U.S. Pat. Nos. 2,283,802, 3,322,868, 4,080,915 and 4,863,660. They suffer from drawbacks due essentially to the presence of the mandrel used during needling.
For example, in U.S. Pat. No. 4,080,915 where the support is rigid, provision is made for it to have openings so as to enable the point of the needle to penetrate therein without breaking. It will be observed that such a solution puts a severe constraint on needling options since the number of openings formed in the support is necessarily limited and it is essential for said needle to aim at such an opening on each stitch. Thus, in this prior patent, provision is made for the openings to be elongated slots, and for the lines of stitching to be rectilinear and in correspondence with said slots. It can thus be seen that not only must the density of stitches over the substrate be small, but also that the shapes of the lines of stitches and the distribution of the stitches are defined once and for all by said openings.
In contrast, in U.S. Pat. No. 4,863,660, provision is made for the support to be of a foam material or the like, thereby enabling the point of the needle to penetrate therein. Under such circumstances, there is no longer any limitation on stitch density or on the shapes of lines of stitching; however, it is then necessary for the support to be made of a material that is easily destroyed so as to enable the substrate to be disengaged from said support.
Methods of making hollow reinforcing members from fibers are also known in which a mandrel is not required; the methods consist of in weaving fibers around rods or sticks which form an array. Such weaving methods are described, for example, in French Patent Nos. 2,395,340, 2,529,589 and 2,531,459. Under such circumstances, the machines built for implementing such methods are complex and expensive. In addition, the kind of weave obtained is determined by said array of rods.